Draft tube



G. A. JEssoP DRAFT TUBE May 7, `19 29.

Filed June 17, 1927 3 Sheets-Sheet l May 7, 1929. l G. A, JEssoP l 1,711,892

DRAFT TUBE Filed June 17, 1927 :s sheets-shea 2 Gage f7. fesso/ G. A. JESSOP DRAFT TUBE May 7, 1929.

3 Sheets-Sheet Filed June 17, 1927 Patented May 7, 1929.

UNITED STATES "PATENT OFFICE.

GEORGEA. JESSOP, F YORK, PENNSYLVANIA, ASSIGNOR TO S. MORGAN SMITH COM- PANY, INC., OF YORK, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

DRAFT TUBE.

Application filed June 1'?,l

This invention relates to draft tubes, and particularly to the elbow type formed of concrete or other analogous material or in some instances formed of metal. The pres 5 ent invention embodies an improvement of the structure disclosed by my pending appli* cation filed March 11, 1925, Serial No. lll-,850. The same obvious structural advantages in operation in draft tube structure are sought and desired to be maintained in the present structure as in my original improved elbow draft tube disclosed by the aforesaid application, the material variation in the structure of the outlet leg of the tube and a more efficient result in operation being the distinguishing features of the present improvement. It has been discovered that there is a higher velocity at the bottom and outside edges of the tube than at the top center from points 'st-artingwell into the down stream curvature of the elbow and continuing to the outlet of the tube., This variation in velocity begins shortly after the tube starts to bend, and becomes a maximum at or near the end of the elbow7 and then decreases towards the outlet. In order to obtain the best possible efficiency in a draft tube of the elbow, or any other type, it has been found necessary to so form the tube that the water remains in full 'flowing contact with all surfaces of the tube which is accomplished to a very material extent by my novel curvature of the elbow in this class of elbow draft tubes, and as specified in my aforesaid application. ln accordance with the features of'this improvement a more efficient and complete or full flowing contact with the surface of the outlet leg of the tube is obtained by filling in the top of the tube at the center along thev horizontal leg and for a f distance upwardly into theJ downstream portion of the elbow top curve, and thereby overcome the formation in the'tube of a comparatively dead space at the center and top of the horizontal leg or outlet portion of the tube, and thereby secure a more even distribution of water in all parts Vof the tube. As vthe rwater lflows downwardly through the tube fromr the entrance and is gradually turned from a vertical direction by the upstream curvature of the elbow, there is a natural spreading'effect 1927. Serial No. 199,530.

which increases and becomes more noticeable at what may be termed each section of the elbow organization. At the beginning of the upstream curvature of the elbow section the spreading effect is slight and becomes greater in the successive portions or sections thereof until it reaches its maximum at or near the final section where t-he elbow merges into the outlet or horizontal leg of the draft tube. The velocities in these tubes, particularly when used for turbines under very large heads, are quite high, andthe spreading action is therefore quite rapid and causes a large portion of the water to pass to the outside curved periphery of the tube at the final sections of the elbow or near the terminal ofthe latter situated adjacent to the horizontal leg of the tube outlet. The water at the outside of the tube is therefore assuming a spiral motion but flows forwardly along the tube at a more rapid rate than Vitsrate of spiral revolution, the spiral movement of the water being insufficient to force or throw the water to the center of the tube and permitting a void to be formed at the center of the tube, whichk should be filled or rectified by change of shape of the tube to eliminate eddies and partial voids.

The general operationof the present tube within the length 'of the curvature complete y is the same as that disclosed in my pending *applicationy above noted, but in the improved structure there is a modification of structureto attain a more satisfactory and complete Loperation -andthereby overcome the slight disadvantages present in my prior structure. rIphe improvementas set forth in this application is particularly advantageous where it is desirable to install elbow draft tubes of comparatively small vert-ical ing in, or reducing the area by fmeans of an obtuse triangular pad or inverted arch,

with, preferably approximately straightY sides. The height or extent of this pad is a maximum at the center of the tube and decreases to nothing at the sides or where it joins the fillets at the upper outsider portions of the elbow bend. In some cases where this improvement is used, it will be necessary to make the outside portions of the elbow bend, near its termination, of a greater vertical extent than would be used with a tube constructed according to my co-pending application, Serial No. 14,850, in order to provide a draft tube with an increasing area in the direction of flow from the inlet to the outlet of the tube, or', at the limit, to pr'ovide a draftftube that does not decrease in area at or near the end of the elbow bend. In some cases, it may be desirable to make the tube with a constant area for a comparatively short distance, in the vicinity of the end of the elbow bend. It is not intended that the improved draft tube be limited to any particular rate of increase of area or' to any particular rate of decrease of velocity. Further, in' the present improved structure, wherever it is possible, this inverted varch roof portion embodies a straight line construction and the curved, or circular, sides of the prior structm'e are replaced with vertical sides, sometimes with straight fillets at the farthest possible upstream section of the tube consistent with satisfactory results. This simplifies and cheapens the work required to construct the tubes, whether made of concrete, metal or other material.

The present object of this invention therefore, is the provision of an inverted arch roof or top portion for the horizontal leg of the draft tube'to obtain a more uniform velocity at the outlet of the tube, and to secure a uniformity of flow of water with the greatest possible reduction in velocity from the entrance of the draft tube to the outlet of the tube, and whereby the formation of a dead space at the center and top of the horizontal leg` is entirely avoided and a more even distribution of the water over the remaining passage is obtained, thus overcoming the disadvantage of having the water break away in the top or downstream curve of the elbow.

The present invention consists essentially in the preferred general construction and arrangement of parts which will be more fully hereinafter described and claimed.

The accompanying drawings 'illustrate the improved draft tube formed of concrete or analogous cementitious material, but it will be understood that the same essential features of invention may be included in a metal or sheet steel draft tube.

In the drawing Fig. 1 is a transverse vertical section through a draft tube embodying the improved features of the invention, the difference in construction being illustrated atv the outlet or horizontal leg of the draft tube, and indicated by a dotted line.

Fig. 2 is a horizontal section 2. 2. Fig. 1.

Fig. 3 is a horizontal section 3. 3. Fig. 1.

Fig. l is a transverse section 4t. t. Fig. 1.

Fig. 5 is a transverse section 5. 5. Fig. l.

Fig. 6 is a transverse sectionon the line G. (i. Fig. 1.

Fig. 7 is a partial transverse section on the line 7. 7. Fig. 1.

Fig. 8 is a partial transverse section on the line 8. 8. Fig. 1.

on the line on the line on the line Fig. 9 is a transverse section on the line 9. 9. rig. 1.

Fig. 10 is a transverse section on the line 10. 10. Fig. 1.

Fig. 11 is an end elevation of the outlet leg.

'lhe'numeral 5 designates a concrete or other cementitious structure in which the improved tube is suitably formed, the latter .omprising an upper inlet extremity 6 Vover which the runner or wheel is adapted to be mounted in the usual manner. The concrete or other analogous structure 5 may be continued upwardly any suitable distance to serve as a base support for the installation of the remaining part of a turbine or other water power organization, and also for the purpose of supporting a power house in which the turbine unit or units are disposed. The upper member 7 of the imgroved draft tube is shown as composed of sheet metal down to the point 8, the remainmg part of the draft tube being shaped in the concrete or other material. It will be understood that the upper member 7 of the draft tube, which may be specified as the inlet member may in some instances be constructed or shaped in the concrete. his upper inlet member 7 to a point a short distance below'the plane of section 2. 2. is concentric with relation to the axial line 9 which is also the vertical axis of the runner or wheel and the turbine shaft. The upper inlet member 7 may be slightly bowled and regularly flares in a downward direction as shown or it may have a straight taper or flare. At a comparatively short distance below the plane or section on the line 2. 2. and as indicated by the plane of section 3. 3. Fig. 3, the draft tube begins to assume an elliptical contour, and `this vconfigurati.on increases gradually in the present instance through to the plane of the section 6. 6., as indicated by Figs. 3 to 6 inclusive. In order to arrive at this construction, the curve 11 of the upstream or lower side of the elbow begins prior to the curve 12 of on the line the downstream or forward upper wall of the draft tube elbow. The rear orv upstream curve 11 comes from the vertical to the hori- Zontal in an arc with a practically constant radius, or in other words, with a constanty curvature. The curvature of the downstream or upper face of the elbow starts at a materially lower elevation than the upstream curve 11 when considering a vertical tube construction only. 1n other words, the curvature 12 of the downstream face of the elbow in the downstream direction starts much later than the curvature 11 ofthe upstream face. This downstream curve 12 of the upstream face is an easement curve, that is, at the beginning thereof there is a long radius of curvature and this radius is gradually decreasedand becomes' a mini-` mum at or near the end of the curve, as at 9, for the outside portions of the tube and, as at 13, for the central portion of the tube. ln a vertical setting the points are about at the horizontal. From the point of the plane of the section 7. 7. to the point 13 or end of the easement curve there is a modiiication of structure in the present improved invention relatively lto that disclosed in my prior application heretofore noted for ythe f purpose of assisting the water to remain in a more perfect full flowing contact with the downstream or. upper portion of the elbow of the draft tube, and assist in maintaining a practically equal velocity of water at a given section of the draft tube. The maintainance of an equal velocity at all points in a given section of a draft tube, said seo' tion being taken approximately at right angles to the longitudinal center line, is necessary in .order to maintain smooth flow and high efficiency in the tube. Again, for the purpose of illustration, let it be assumed rthat the tube is divided into three distinct widthv is meant the distances between the walls of the tube as measured at right angles to the foregoing plane, each measurement passing through the longitudinal center line of the tube.

The second part of the tube is the curve or elbow section 10. rllhe breadth of the tube is a maximum at` approximately the end of the first part, and atapproximately the beginning of the second part or section or elbow 10. The breadth of the second part or elbow member 10 relatively decreases from its maximum Vat the entrance of this second part or section to its minimum at or near the end of the elbow, as at 9 and 13. In other words,lthe upstream or lower face of the draft tube defined by the curve 11 approaches and gets nearer to the downstream or upper face of the draft tube defined by the curve 12. At the same time the width or lateral extent ofthe draft tube is increased all along the bend or elbow section 10, and this increase is such that the area of the tube is constantly increasing, so that the velocity of the water in the tube is constantly decreasing, or the velocity head is constantly being converted into pressure head. rPhe reduction in the breadth of the tube from the beginning of the upper end of the second section or part or elbow 10 is accomplished by making a curvature of the upstream and downstream faces of the tube, or the lower and upper sides of the tube, in the curvature heretofore specified, and further because the curvature of the downstream or upper face or side is started at a considerably lower point or later'than the curvature ,of the upstream orlower face.

The third part of the sectional tube is the horizontal leg 15 which serves as the outlet. Both the breadth and width yof this leg may increase gradually, but it is unnecessary that both increase, in vie-w of the fact that one dimension, for instance, the vertical extent of the leg, could remain constant and even be decreased, provided the width or lateral extent of the tube be increased a sufficient degree to maintain the continuously increasing area as the water approaches nearer and nearer the outlet end. 16. As hereinbefore indicated, from the entrance of the improved tube to the outlet end thereof the area is continuously increasing and therefore the velocity of the. water is continuously decreas- The present improvement, in view of my prior structure, preserves in the main Vthe same structural conditionA `inst enumerated with structural modification or changes in the upper part ofthe outlet leg or section 15 and a continuance of the same change into the downstream part of the elbow as far upwardly as about the plane of the section indicated by the line 7. 7. shown by Figure 1, and which consists in directing the curve 17 at the center of the downstream easement portion of the tube with a longer series of radii than the similar easement curve represented by the hight hand end of the dotted line 17a, inthe construction of the elbow described by my' aforesaid application` at the downstream'or upper portion of the said elbow and than the similar. curve used in the construction of the present elbow at the outside portions of the elbow bend, the said curve 17 continuing to depart regularly from the curve 17n until it reaches about the point 13 where it gradually merges into a flattened top portion 18 of the outlet leg 15 which is substantially below the line 17a which line indicates the height of the central portion of the top of the draft tube outlet leg as shown in my said prior application. At about this point 13 is the rear terminal of a supporting pier 19 which is located in the center of the horizontal outlet leg 15 and continues fully to the outlet end 16 of the leg. As indicated by the cross sections, in Figures 9, 10 and 11, the fiat top converges from opposite sides, as at 20, Figure 9, 21, Figure 10, and 22, Figure 11, equally towards the center of the leg of the tube, the section 9 being adjacent to the lower terminal of the curve 17, and the said inward convergence, as at 20, at opposite side port-ions of the tube in the lower extremity of the elbow starts a little to the rear of the plane of the cross section, as illustrated by Figure 9 or nearly as far back inwardly and upwardly as the plane of the section 7, and gradually the convergence increases in angularity or has a greater dip towards the center from opposite sides, as illustrated by Figures 10 and 11. As shown by Figure 9, the opposite sides of the elbow, as at 23, are curved to form fillets where these sides join the top and bottom walls, but this curvature gradually merges or is changed into a more nearly straight or vertical side structure, as at 24, Figures 10 and 11, and the angular corners formed by the intersections of the outer extremities of the upwardly inwardly conyerging portions 21 and 22 as shown by Figures 10 and 11 and the bottom 25 are filled by fillets 26 throughout the whole length of the leg 15. Hence the outlet leg 15 of this improved draft tube as compared to my prior improved structure is filled in the center of its top portion to the depth shown between lines 172L and 18 and thus materially aids in overcoming the tendency of the water to break away from the top or downstream curve of the elbow at the plane of the seczions 8 and 9, and eliminating from the tube the comparatively dead space at the center and top of the horizontal leg 15 and obtaining a more even distribution of the water, over the remaining passage and also avoiding any tendency to spiral motion of the water along the side portions of the leg, the latter ha\.'ing at the top thereof a straight line construction of inverted arch contour. This improved construction not only results in a more satisfactory full tiowing contact of the water at the opposite sides of the leg without any tendency towards spiral movement and a consequent elimination of eddy formation and void spaces, but also simpliiies and cheapens the form work required to cast these draft tubes in the concrete. This improved structure of elbow draft tube produces full flowing water contact with all surfaces throughout the length of the tube, and the water is gradually decelerated towards the outlet end 1G of the tube, and is finally discharged into the tailrace.

W hat is claimed as new is 1. A draft tube having an inlet extremity concentric with relation to a central axis and continuing into an elbow which is gradually decreased in breadth from. the upstream towards the downstream portion thereof by an upstream, practically constant radius curve and a downstream easement curve, the draft tube being increased in width and terminating in an out-let extremity having a top portion which is lower at its center than at its sides.

2. A draft tube having an inlet extremity concentric with relation to a central'axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by means of an upstream, practically constant radius curve and a downstream easement curve and proportionately laterally increased in width and terminating in an outlet leg, the said outlet leg having a top portion which slopes downwardly towards its center and having opposite vertical sides, the draft tube from its inlet to its outlet extremity increasing in area.

3. A draft tube comprising an inlet member and an outlet leg with an elbow therebetween, the said elbow being decreased in breadth from the upstream towards the d ownstreamfportion thereof by means of an upstream, practically constant radius curve and a downstream easement curve, said easement curve starting at a materially lower elevation than said constant radius curve and the said elbow bend being correspondingly and proportionately increased 1n width, the outlet leg having a flattened top portion in the form of an inverted arch.

el. A draft tube having inlet and outlet extremities with an elbow bend therebetween, the inlet extremity being circular and the tube as an entirety from itsinlet extremity being increased in lateral extent and continuing with this lateral increase throughout the elbow in a direction from the upstream towards the downstream portion of said bend, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve, the outlet extremity havingva flattened top portion with members converging towards the center from opposite sides of the said outlet extremity.

5. A draft tube having inlet and outlet extremities with an elbow bend therebetween, the inlet extremity being circular and the tube as an entirety from its inlet extremity being increased in lateral extent and continuing with this lateral increase through the elbow in a direction from the: upstream towards the downstream portion of said bend, the elbow bend havingan upstream, practically constant radius curve and a downstream easement curve, thev outlet extremity having a flattened top portion with members converging' towards the center from opposite sides of the said outlet extremity, the sides of th'e outlet vextremity being vertically straight.

6. A draft tube having inlet and outlet extremities with Aan elbow bend therebetween and gradually increased in lateral extent from the inlet extremity which is circular in contour to the outlet leg at a distance beyond the termination of the elbow bend, the elbow bend correspondingly and gradually increasing in lateral extent throughout the formation thereof towards the outlet extremity, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve, the elbow bend gradually decreasing in transverse vertical extent towards theoutlet extremity, and' the outlet extremity having a flattened top which continues with diminishing structure partially `into the upper downstream side of the elbow.

v7. A draft tube having inlet andV outlet extremities with an elbow bend interposed between said extremities and continuous therewith, the said elbow being materially liattened in a. transverse vertical direction within the area of the bend from the upstream towards the dowistream` portion thereof and also increasing in width within the area of the bend and regularly continuing into the outlet extremity, the elbow bend l having an upstream, practically constant radius curve and a downstream easement curve of transversely flattened contour in the form of an inverted arch and having i vertical sides with lillets in the upper and lower angles of the same.

8. A draft tube having` inlet and outlet extremities and an elbowA bend between the two extremities, the inlet extremity Abeing concentricpwith relation to a central axis and regularly Vcontinuing into the elbow bend, the elbow bend regularly decreasing in breadth by an upstream substantially constant radius curve'and a downstream easement v curve, differing from the' upstream curve, the said bend also positively increasing in width divergently, and said divergence regularly and fully continuing to the outlet xtremity of the tube, the outlet extremity of the tube having flattened top and side' portions, the `flattened 'top portion ofthe outlet extremity extending a distance rearwardly into the elbow bend, and the opposite curved sides of the bend 'merging into straight vertical sides of the said outlet extremity, the said outlet extremity `also having a centrally disposed longitudinally arranged pier therein fully from the top to the bottom of said extremity.

9. Adraft tube havingvinlet and outlet extremities and anelbow bend between the extremities, said elbow bend at the upstream portion having a curve which comes fromv the vertical to the horizontal in an arc of a circle, and the opposite or downstream portion having an easement curve which is formed in the center with a dip towards and merging into the top of the outlet extremity when it is decreased in height at the center and providing an easement curve with less rapid change of curvature in the center than at' the outside portions which continues into the outlet extremity to decrease the breadth of the elbow bend in a direction from the upstream towards the downstream portion of the tube, the latter being proportionately increased in width through they elbow, the outlet extremity being decreased in vertical extent at the center. l

v l0. A draft tube having inlet and outlet extremities and an elbow bend between the extremities, said elbow bend at the upstream portion having a curve which comes from the vertical to the horizontal and the opposite or downstream portion having a curve which is .formed with a dip towards and merging into the top of the outlet extremity and providing'an easement curve with less rapid change of curvature in the center than at the outside portion and continuing into the outlet extremity to decrease the breadth of the bend in a direction from the upstream ltowards the downstream portion of the tube and proportionately increase the said width of the tube at the elbow, the outlet extremity being formed with a flat-tened top portion in thev form of an inverted arch having a central longitudinally extending dividing pier which terminates at itsv inner end at the outerterniination of the, elbow curve.

ll.. A draft tube having inlet and outlet extremities with an elbow bend therebetween, the inlet extremity being circular and the tube as an entirety from its inlet extremitybeing increased in lateral extent and continuing with this lateral increase through the elbow in a direction from the'upstream towards the downstream portion of said bend, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve, the outlet extherewith, the said elbow being materially curve and a downstream easement curve of flattened in a transverse vertical direction flattened contour which is transversely within the area of the bend portion thereof straight and having vertical sides with lillets 10 andalso increasing in width within the area in the upper andlower angles of the same.

of the bend and regularly Continuing into In testimony whereof l have hereunto set the outlet extremity, the elbow bend having my hand.

an upstream, practically constant radius GEORGE A.. JESSOP. 

